The present invention relates generally to an image display system for producing a color image by arranging a color shutter capable of time-divisionally switching a plurality of colors to be displayed, in front of a monochrome image display, and an image display method using the image display system.
As a method for displaying a color image, it is usually well carried out to synthesize images of red (R), green (G) and blue (B), which are three primary colors of light, or to divide the images. Such an image synthesizing method for displaying images is divided into a space sharing display for two-dimensionally arranging dots for R, G and B to spatially arrange an image, and a time sharing display for displaying R, G and B images in time series. Typically, color cathode ray tubes and liquid crystal displays use the space sharing display since R, B and G pixels are two-dimensionally arranged. Similarly, in the case of an image pickup, there are adopted methods for spatially arranging R, G and B color filters and for providing a color filter, which is capable of changing display colors in time series, in front of an image pickup element. A process for displaying an image will be briefly described below.
The time sharing display is achieved by quickly switching display colors on the whole display surface in synchronism with the display for R, G and B images by means of R, G and B color filters or the like. It is necessary for the time sharing display to switch the display for images at a higher speed than three times as high as that in the spatial sharing display. However, it is not necessary for the time sharing display to divide a pixel into parts for R, G and B images, so that it is possible to achieve a higher definition image. As a method for switching the display color, there is known a method for mechanically rotating a disc-like color filter which is divided into equal three parts and which is color-coded. As a method for electrically switching the display color, Bos, et al. proposes a technique in Japanese Patent Publication No. 4-49928, which discloses a so-called liquid crystal color shutter, which comprises two liquid crystal cells and color polarizing plates arranged on both sides thereof, for switching ON/OFF of the liquid crystal cells to control the plane of polarization for light to select the wavelength of light absorbed into the polarizing plates to display R, G and B. This liquid crystal color shutter has advantages in that there are no mechanical operations, the area of the color shutter can be equal to the area of the display screen to reduce required space, and so forth.
In the liquid crystal color shutter, the absorption axes of a plurality of color polarizing plates are perpendicular to each other. The two liquid crystal cells are turned ON and OFF to directly transmit the polarized light of an incident light or, to rotate the polarized light by 90 degrees to transmit or absorb specific wavelength components, so that a desired display color can be obtained. One of conventionally proposed liquid crystal color shutters is a PI cell having a bend alignment. This can achieve a higher response speed than that of a TN (twisted nematic) cell, which is generally used as a liquid crystal display, i.e., a response time of about 2 ms.
On the other hand, in the case of the time sharing display, there is caused a so-called xe2x80x9ccolor breakupxe2x80x9d interference wherein the profile of a display image appears to be iridescent due to observer""s blink, the movement of observer""s eye, the movement of an object on a dynamic image, and so forth. In order to reduce the color breakup interference, it is desired to increase the switching speed for R, G and B to switch R, G and B as much as possible in a predetermined period of time such as one field period. For example, in the case of a triple speed display for displaying each of subfields R, G and B once in one field period, the display period for each color is 1/(60 Hzxc3x973)=5.6 ms assuming that one field is 60 Hz. Here, one field period is defined as a period necessary for completing one color picture in spite of interlace or non-interlace display. For example, one field corresponds to 60 Hz in the case of an NTSC (National Television System Committee) color system for performing the interlace display.
However, if the frequency of subfields R, G and B displays in one field period is intended to increase in order to more reduce the color breakup interference, the response speed of the PI cell is not sufficient as shown in FIG. 1, so that it is required to provide a switching element having a higher response time. For example, when each of subfields R, G, B is displayed twice in a field of 60 Hz, the subfield period for each color is 1/(60xc3x976)=2.8 ms. When 2 ms serving as a response time of the PI cell is subtracted from the display period for each color, it is possible to ensure only 800 xcexcs, which is 28% of the whole display period for each color, as an appropriate display time.
As described above, in the case of the conventional time sharing type display system using the liquid crystal color shutter, there are problems in that the cell itself of the liquid crystal color shutter does not have a sufficient response time, so that a color breakup interference is caused.
It is therefore an object of the present invention to eliminate the aforementioned problems and to provide an image display system and image display method, which can ensure a sufficient response time of cells of a liquid crystal color shutter in a time sharing display system for reducing a color breakup interference.
In order to accomplish the aforementioned and other objects, according to a first aspect of the present invention, there is provided an image display system for producing a color image by arranging a color shutter capable of time-divisionaly switching a plurality of colors to be displayed, in front of a monochrome image display, the image display system comprising: self-luminous image display means for time-divisionally displaying monochrome images corresponding to three primary colors; and color display means for time-divisionally coloring and outputting the monochrome images which formed on the side of a light outgoing surface of the self-luminous image display means and which correspond to the three primary colors, the color display means comprising a liquid crystal cell driven by carrying out an optical switching on the basis of the inversion between positive and negative polarities of the applied voltage, a transparent electrode formed by dividing the liquid crystal cell into a plurality of parts, and a liquid crystal color shutter capable of optionally setting display colors for a plurality of display regions by means of the transparent electrode, the liquid crystal color shutter displaying different display colors for at least two display regions in an optional time in a driving condition.
According to a second aspect of the present invention, in the image display system according to the first aspect, the self-luminous image display means is monochrome luminescent display means for displaying a monochrome image by a line scanning, the monochrome luminescent display means comprising at least one of a monochrome CRT (Cathode Ray Tube), a monochrome EL (Electro-Luminescent) display element, an FED (Field Emission Display) and a PDP (plasma display element), which have a frequency F necessary to display all of screens corresponding to the three primary colors, and the monochrome luminescent display element having a phosphor having an 1/10 afterglow time which is a reducing time xcfx84, in which a peak density of luminescent becomes 1/10, meeting the following relationship:
xcfx84xe2x89xa6{(1/4xe2x88x921/3n)/NFxe2x88x92T}/2
assuming that the liquid crystal color shutter has n divided display regions, a frequency for repeatedly displaying three primary colors for a field period 1/F derived from the frequency F being N, and a response time of the liquid crystal color shutter being T.
According to a third aspect of the present invention, in the image display system according to the first aspect, the liquid crystal color shutter displays four colors including red, green and blue in each field period, and the total of display periods for each color in each field period is equal to each other.
According to a fourth aspect of the present invention, in the image display system according to the third aspect, a fourth display color other than the red, green and blue are displayed in switching periods between the red, green and blue.
According to a fifth aspect of the present invention, there is provided an image display method for producing a color image using an image display system wherein a color shutter capable of time-divisionally switching a plurality of colors to be displayed is arranged in front of a monochrome image display, the image display method comprising a step of time-divisionally displaying monochrome images corresponding to three primary colors using self-luminous image display means; and a step of time-divisionally coloring and outputting the monochrome images, which are formed on the side of a light outgoing surface of the self-luminous image display means and which correspond to the three primary colors, using color display means; wherein the time-divisionally displaying step further includes a sub-step optionally setting display colors for a plurality of display regions by means of a transparent electrode which is driven by carrying out an optical switching on the basis of the inversion between positive and negative polarities and which is formed by dividing a liquid crystal cell forming the color display means into a plurality of parts; and a sub-step of displaying different display colors for at least two display regions in an optional time in a driving condition, using a liquid crystal color shutter formed by the transparent electrode.
According to a sixth aspect of the present invention, in the image display method according to the fifth aspect, the self-luminous image display means is monochrome luminescent display means for displaying a monochrome image by a line scanning, the monochrome luminescent display means comprising at least one of a monochrome CRT, a monochrome EL luminescent display element, an FED and a plasma display element, which have a frequency F necessary to display all of screens corresponding to the three primary colors, and the monochrome luminescent display element having a phosphor having an 1/10 afterglow time xcfx84 meeting the following relationship:
xcfx84xe2x89xa6{(1/4xe2x88x921/3n)/NFxe2x88x92T}/2
assuming that the liquid crystal color shutter has n divided display regions, a period for repeatedly displaying three primary colors for a field period 1/F derived from the frequency F being N, and a response speed of the liquid crystal color shutter being T.
According to a seventh aspect of the present invention, in the image display method according to the fifth aspect, the liquid crystal color shutter displays four colors including red, green and blue in each field period, and the total of display periods for each color in each field period is equal to each other.
According to an eighth aspect of the present invention, in the image display method according to the seventh aspect, a fourth display color other than the red, green and blue are displayed in switching periods between the red, green and blue.
Furthermore, the liquid crystal cell according to the first or fifth aspect may be a liquid crystal cell of spontaneous polarization, such as an FLC (ferroelectric liquid crystal) or an AFLC (antiferroelectric liquid crystal cell, or a liquid crystal cell having a chiral smectic liquid crystal or a DHF (deformed helix ferroelectric liquid crystal).
Moreover, the processing speed may increase as the variation of the frequency N for repeating the display for the three primary colors according to the second or sixth aspect. It is possible to achieve triple speed when N=1, sixfold speed when N=2, and ninefold speed when N=3 in comparison with a field frequency in a time sharing display.